Weldable, coated metal substrates and methods for preparing and inhibiting corrosion of the same

ABSTRACT

The present invention provides a weldable, coated metal substrate having a pretreatment coating including a reaction product of at least one epoxy-functional material and at least one phosphorus-containing material or amine-containing material and a weldable coating having an electroconductive pigment and a binder deposited thereon.

FIELD OF THE INVENTION

This invention relates generally to weldable, corrosion-resistant coatedmetal substrates and, more particularly, to metal substrates havingchrome-free coatings thereon which inhibit corrosion and facilitateforming and welding of the metal substrate.

BACKGROUND OF THE INVENTION

Weldable coatings containing an electrically conductive material, suchas zinc, are often used to provide an electroconductive layer on metalsubstrates. Zinc-rich weldable coatings can be applied directly toferrous metal surfaces or over ferrous metal which has been treated witha chromium-containing solution. For example, U.S. Pat. No. 4,346,143discloses a process for providing corrosion protection to ferrous metalsubstrates comprising etching the surface of the substrate with nitricacid followed by applying a zinc-rich coating including a bindermaterial to the etched surface.

U.S. Pat. Nos. 4,157,924 and 4,186,036 disclose a weldable coating formetallic substrates which contains an epoxy or phenoxy resin,electroconductive pigment such as zinc and a diluent such as glycolether. As discussed at column 7, lines 37-42, the substrate can bepretreated with a pulverulent metal-free composition containing chromateand/or phosphate ions.

Similarly, European Patent Application No. 0157392 discloses ananti-corrosive primer for metal phosphate- or chromate-treated steelwhich consists of a mixture of 70 to 95 weight percent zinc, aluminum, agliding agent and a binding agent.

U.S. Pat. No. 3,687,739 discloses a weldable composite coatingcomprising (1) an undercoating of pulverulent metal and a hexavalentchromium-containing liquid composition and (2) a topcoating comprising aparticulate, electrically conductive pigment and a binder material.

Although chromium-containing coatings provide excellent corrosionprotection, particularly under zinc-rich coatings, they are toxic andpresent waste disposal problems. Therefore, there is a need forchromium-free treatment solutions for treating metal substrates prior tothe application of a weldable coating. The treatment solution shouldprovide corrosion resistance, maintain substrate electroconductivity forwelding and provide lubricity to assist in forming and stamping.

SUMMARY OF THE INVENTION

One aspect of the present invention is a weldable, coated metalsubstrate comprising: (a) a metal substrate; (b) a pretreatment coatingcomprising a reaction product of at least one epoxy-functional materialand at least one material selected from the group consisting ofphosphorus-containing materials, amine-containing materials and mixturesthereof deposited upon at least a portion of a surface of the metalsubstrate; and (c) a weldable coating comprising an electroconductivepigment and a binder deposited upon at least a portion of thepretreatment coating.

Another aspect of the present invention is a weldable, coated metalsubstrate comprising: (a) a metal substrate; (b) a pretreatment coatingcomprising at least one ester of a phosphorus-containing materialdeposited upon at least a portion of a surface of the metal substrate;and (c) a weldable coating comprising an electroconductive pigment and abinder deposited upon at least a portion of the pretreatment coating.

Yet another aspect of the present invention is a method for preparing aweldable, coated metal substrate, comprising the steps of: (a) treatinga surface of a metal substrate with a pretreatment coating comprising areaction product of at least one epoxy-functional material and at leastone material selected from the group consisting of phosphorus-containingmaterials, amine-containing materials and mixtures thereof to form asubstrate having a pretreated surface; and (b) applying a weldablecoating to the pretreated surface to form a weldable, coated metalsubstrate, the weldable coating comprising an electroconductive pigmentand a binder.

Another aspect of the present invention is a method for inhibitingcorrosion of a metal substrate comprising: (a) treating a surface of ametal substrate with pretreatment coating comprising a reaction productof at least one epoxy-functional material and at least one materialselected from the group consisting of phosphorus-containing materials,amine-containing materials and mixtures thereof to form a substratehaving a pretreated surface; and (b) applying a weldable coating to thepretreated surface to form a corrosion-resistant coated metal substrate,the weldable coating comprising an electroconductive pigment and abinder.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The metal substrates used in the practice of the present inventioninclude ferrous metals, non-ferrous metals and combinations thereof.Suitable ferrous metals include iron, steel, and alloys thereof.Non-limiting examples of useful steel materials include cold rolledsteel, galvanized (zinc coated) steel, electrogalvanized steel,stainless steel, pickled steel, zinc-iron alloy such as GALVANNEAL, andcombinations thereof. Useful non-ferrous metals include aluminum, zinc,magnesium and alloys thereof, such as GALVALUME and GALFAN zinc-aluminumalloys. Combinations or composites of ferrous and non-ferrous metals canalso be used.

The shape of the metal substrate can be in the form of a sheet, plate,bar, rod or any shape desired. Preferably, the shape of the metalsubstrate is an elongated strip wound about a spool in the form of acoil. The thickness of the strip preferably ranges from about 0.254 toabout 3.18 millimeters (mm) (about 10 to about 125 mils), and morepreferably about 0.3 mm, although the thickness can be greater or less,as desired. The width of the strip generally ranges from about 30.5 toabout 183 centimeters (about 12 to about 72 inches), although the widthcan vary depending upon its intended use.

Before depositing the coatings upon the surface of the metal substrate,it is preferred to remove foreign matter from the metal surface bythoroughly cleaning and degreasing the surface. The surface of the metalsubstrate can be cleaned by physical or chemical means, such asmechanically abrading the surface or cleaning/degreasing withcommercially available alkaline or acidic cleaning agents which are wellknow to those skilled in the art, such as sodium metasilicate and sodiumhydroxide. A non-limiting example of a preferred cleaning agent isCHEMKLEEN 163 phosphate cleaner which is commercially available from PPGIndustries, Inc. of Pittsburgh, Pa.

Following the cleaning step, the metal substrate is usually rinsed withwater, preferably deionized water, in order to remove any residue. Themetal substrate can be air dried using an air knife, by flashing off thewater by brief exposure of the substrate to a high temperature or bypassing the substrate between squeegee rolls.

In the present invention, a pretreatment coating is deposited upon atleast a portion of the outer surface of the metal substrate. Preferably,the entire outer surface of the metal substrate is coated with thepretreatment coating.

The pretreatment coating facilitates adhesion of the subsequentlyapplied weldable coating to the metal substrate. The pretreatmentcoating should be sufficiently thin and/or deformable to permit the heatand force applied to the weldable coating by the welding tool to driveat least a portion of the electroconductive pigment therein through thepretreatment coating to contact or essentially contact the metalsubstrate and provide an electrically conductive path to permit weldingof the coated substrate. As used herein “essentially contact” means thatthe electrical resistance provided by the pretreatment coating is lessthan about 1 ohm. The thickness of the pretreatment coating can vary,but is generally less than about 1 micrometer, preferably ranges fromabout 1 to about 500 nanometers, and more preferably is about 10 toabout 300 nanometers.

In a preferred embodiment, the pretreatment coating comprises a reactionproduct of one or more epoxy-functional materials and one or morematerials selected from phosphorus-containing materials,amine-containing materials and mixtures thereof.

Useful epoxy-functional materials contain at least one epoxy or oxiranegroup in the molecule, such as monoglycidyl ethers of a monohydricphenol or alcohol or di- or polyglycidyl ethers of polyhydric alcohols.Preferably, the epoxy-functional material contains at least two epoxygroups per molecule and has aromatic or cycloaliphatic functionality toimprove adhesion to the metal substrate. Further, it is preferred thatthe epoxy-functional materials be relatively more hydrophobic thanhydrophilic in nature.

Examples of suitable monoglycidyl ethers of a monohydric phenol oralcohol include phenyl glycidyl ether and butyl glycidyl ether. Usefulpolyglycidyl ethers of polyhydric alcohols can be formed by reactingepihalohydrins with polyhydric alcohols, such as dihydric alcohols, inthe presence of an alkali condensation and dehydrohalogenation catalystsuch as sodium hydroxide or potassium hydroxide. Useful epihalohydrinsinclude epibromohydrin, dichlorohydrin and epichlorohydrin (preferred).Suitable polyhydric alcohols can be aromatic, aliphatic orcycloaliphatic.

Non-limiting examples of suitable aromatic polyhydric alcohols includephenols which are preferably at least dihydric phenols. Non-limitingexamples of aromatic polyhydric alcohols useful in the present inventioninclude dihydroxybenzenes, for example resorcinol, pyrocatechol andhydroquinone; bis(4-hydroxyphenyl)-1,1-isobutane;4,4-dihydroxybenzophenone; bis(4-hydroxyphenyl)-1,1-ethane;bis(2-hydroxyphenyl)methane; 1,5-hydroxynaphthalene; 4-isopropylidenebis(2,6-dibromophenol); 1,1,2,2-tetra(p-hydroxy phenyl)-ethane;1,1,3-tris(p-hydroxy phenyl)-propane; novolac resins; bisphenol F;long-chain bisphenols; and 2,2-bis(4-hydroxyphenyl)propane, i.e.,bisphenol A (preferred).

Non-limiting examples of aliphatic polyhydric alcohols include glycolssuch as ethylene glycol, diethylene glycol, triethylene glycol,1,2-propylene glycol, 1,4-butylene glycol, 2,3-butylene glycol,pentamethylene glycol, polyoxyalkylene glycol; polyols such as sorbitol,glycerol, 1,2,6-hexanetriol, erythritol and trimethylolpropane; andmixtures thereof. An example of a suitable cycloaliphatic alcohol iscyclohexanedimethanol.

Suitable epoxy-functional materials have an epoxy equivalent weightranging from about 100 to about 500, and preferably about 130 to about250, as measured by titration with perchloric acid using methyl violetas an indicator. Useful epoxy-functional materials are disclosed in U.S.Pat. Nos. 5,294,265; 5,306,526 and 5,653,823, which are herebyincorporated by reference.

Examples of suitable commercially available epoxy-functional materialsare EPON® 826 and 828 epoxy resins, which are epoxy functionalpolyglycidyl ethers of bisphenol A prepared from bisphenol-A andepichlorohydrin and are commercially available from Shell ChemicalCompany. EPON® 828 epoxy resin has a number average molecular weight ofabout 400 and an epoxy equivalent weight of about 185-192. EPON® 826epoxy resin has an epoxy equivalent weight of about 178-186.

Other useful epoxy-functional materials include epoxy-functional acrylicpolymers, glycidyl esters of carboxylic acids and mixtures thereof.

As discussed above, the epoxy-containing material can be reacted withone or more phosphorus-containing materials to form an ester thereof,such as an organophosphate or organophosphonate. Suitablephosphorus-containing materials include phosphoric acids, phosphonicacids and mixtures thereof.

Examples of suitable phosphonic acids include those having at least onegroup of the structure:

ti —R—PO—(OH)₂

where R is —C—, preferably CH₂, and more preferably O—CO—(CH₂)₂—.Non-limiting examples of suitable phosphonic acids include1-hydroxyethylidene-1,1-diphosphonic acid, methylene phosphonic acids,and alpha-aminomethylene phosphonic acids containing at least one groupof the structure:

such as (2-hydroxyethyl)aminobis(methylene phosphonic) acid,isopropylaminobis(methylenephosphonic) acid and other aminomethylenephosphonic acids disclosed in U.S. Pat. No. 5,034,556 at column 2, line52 to column 3, line 43, which is hereby incorporated by reference.

Other useful phosphonic acids include alpha-carboxymethylene phosphonicacids containing at least one group of the structure:

Non-limiting examples of suitable phosphonic acids includebenzylaminobis(methylene phosphonic) acid, cocoaminobis(methylenephosphonic) acid, triethylsilylpropylamino(methylene phosphonic) acidand carboxyethyl phosphonic acid.

Suitable esters of phosphorus-containing materials include β-hydroxyphosphorous esters of any of the phosphoric acid or phosphonic acidsdiscussed above, for example phosphoric acid esters of bisphenol Adiglycidyl ether, benzylaminobis(methylenephosphonic) ester of bisphenolA diglycidyl ether, carboxyethyl phosphonic acid ester of bisphenol Adiglycidyl ether, phenylglycidyl ether and butyl glycidyl ether;carboxyethyl phosphonic acid mixed ester of bisphenol A diglycidyl etherand butylglycidyl ether; triethoxyl silylpropylaminobis(methylenephosphonic) acid ester of bisphenol A diglycidylether and cocoaminobis(methylenephosphonic) acid ester of bisphenol Adiglycidyl ether.

The epoxy-containing material and phosphorus-containing material aretypically reacted in a equivalent ratio of about 1:0.5 to about 1:10,and preferably about 1:1 to about 1:4. The epoxy-functional material andphosphorus-containing material can be reacted together by any methodwell known to those skilled in the art, such as a reversephosphatization reaction in which the epoxy-containing material is addedto the phosphorus-containing material.

Typically, the reaction product of the epoxy-functional material andphosphorus-containing material has a number average molecular weight ofup to about 2000, and preferably about 500 to about 1000, as measured bygel permeation chromatography using polystyrene as a standard.

In an alternative embodiment, the pretreatment coating comprises one ormore esters of a phosphorus-containing material, for example such as arediscussed above. Other suitable esters include the reaction product ofphosphorus pentoxide as P₄O₁₀ and an alcohol in a 1:6 molar ratio ofoxide to alcohol to produce a mixture of mono- and diphosphate esters,such as is disclosed in the 18 Encyclopedia of Chemical Technology,(4^(th) Ed. 1996) at page 772, which is hereby incorporated byreference. Examples of suitable alcohols include aliphatic alcohols suchas ethylene glycol, phenols such as bisphenol A, and cycloaliphaticalcohols.

In an alternative preferred embodiment, the reaction product can beformed from one or more epoxy-containing materials, such as arediscussed above, and one or more amine-containing materials selectedfrom primary amines, secondary amines, tertiary amines and mixturesthereof. Non-limiting examples of suitable primary amines includen-butyl amine and fatty amines such as ARMEEN 18D which is commerciallyavailable from Akzo Nobel. Suitable secondary amines includediisopropanolamine, diethanolamine and di-butyl amine. An example of auseful tertiary amine is ARMEEN DM18D dimethyl C18 tertiary amine.

Preferably, the amine-containing material comprises at least onealkanolamine or a mixture of different alkanolamines. Primary orsecondary alkanolamines are preferred, however tertiary alkanolaminescan be used. Preferred alkanolamines include alkanol groups containingless than about 20 carbon atoms, and more preferably less than about 10carbon atoms. Non-limiting examples of suitable alkanolamines includemethylethanolamine, ethylethanolamine, diethanolamine (preferred),methylisopropanolamine, monoethanolamine and diisopropanolamine.Preferred tertiary alkanolamines contain two methyl groups, such asdimethylethanolamine.

The epoxy-functional material and amine-containing material arepreferably reacted in an equivalent ratio ranging from about 5:1 toabout 0.25:1, and more preferably about 2:1 to about 0.5:1. Theepoxy-functional material and amine-containing material can be reactedtogether by any method well known to those skilled in the art of polymersynthesis, such as solution or bulk polymerization techniques. Forexample, an alkanolamine can be added to an epoxy-functional materialand diluent, mixed at a controlled rate and the mixture heated at acontrolled temperature under a nitrogen blanket or other procedure wellknown to those skilled in the art for reducing the presence of oxygenduring the reaction. Suitable diluents for reducing the viscosity of themixture during the reaction include water; alcohols containing up toabout 8 carbon atoms, such as ethanol or isopropanol; and glycol etherssuch as the monoalkyl ethers of ethylene glycol, diethylene glycol orpropylene glycol.

If a tertiary alkanolamine is used, a quaternary ammonium compound isformed. Typically, this reaction is carried out by adding all of the rawmaterials to the reaction vessel at the same time and heating themixture, usually with a diluent, at a controlled temperature. Usually,an acid such as a carboxylic acid is present to ensure that thequaternary ammonium salt is formed rather than a quaternary ammoniumoxide. Suitable carboxylic acids include lactic acid, citric acid,adipic acid and acetic acid (preferred). Quaternary ammonium salts areuseful because they are more easily dispersed in water and can be usedto form an aqueous dispersion having a pH near the desired applicationrange.

Generally, the reaction product of the epoxy-functional material andamine-containing material has a number average molecular weight of up toabout 1500, and preferably about 500 to about 750, as measured by gelpermeation chromatography using polystyrene as a standard.

A treating solution of one or more of any of the reaction productsdiscussed above can be prepared by mixing the reaction product(s) with adiluent, such as water, preferably at a temperature of about 10° C. toabout 70° C., and more preferably about 15° C. to about 25° C.Preferably, the reaction product is soluble or dispersible in waterdiluent to the extent of at least about 0.03 grams per 100 grams ofwater at a temperature of about 25° C. The reaction product generallycomprises about 0.05 to about 10 weight percent of the treating solutionon a total weight basis.

Useful diluents include water or mixtures of water and cosolvents.Suitable cosolvents include alcohols having up to about 8 carbon atoms,such as ethanol and isopropanol; and alkyl ethers of glycols, such as1-methoxy-2-propanol, dimethylformamide, xylene, and monoalkyl ethers ofethylene glycol, diethylene glycol and propylene glycol. Preferably, thediluent includes a propylene glycol monomethyl ether such as DOWANOL PMor dipropylene glycol monomethyl ether DOWANOL DPM, which arecommercially available from Dow Chemical Company. Other useful diluentsinclude bases such as amines which can partially or completelyneutralize the organophosphate or organophosphonate to enhance thesolubility of the compound. Non-limiting examples of suitable aminesinclude secondary amines, such as diisopropanolamine (preferred), andtertiary amines such as triethylamine, dimethylethanolamine and2-amino-2-methyl-1-propanol. Non-aqueous diluents are typically presentin amount ranging from about 0.1 to about 5 weight percent on a basis oftotal weight of the treating solution. Water can be present in amountranging from about 50 to about 99 weight percent on a basis of totalweight of the treating solution.

Typically, water-soluble or water-dispersible acids and/or bases areused to adjust the pH of the treating solution to about 2 to about 8.5,and preferably about 2.7 to about 6.5. Suitable acids include mineralacids, such as hydrofluoric acid, fluoroboric acid, phosphoric acid, andnitric acid; organic acids, such as lactic acid, acetic acid,hydroxyacetic acid, citric acid; and mixtures thereof. Suitable basesinclude inorganic bases, such as sodium hydroxide and potassiumhydroxide; nitrogen-containing compounds such as ammonia, triethylamine,methanolamine, diisopropanolamine; and mixtures thereof.

Preferably the treating solution further comprises a fluorine-containingmaterial as a source of fluoride ions. Suitable fluorine-containingmaterials include hydrofluoric acid, fluorosilicic acid, fluoroboricacid, sodium hydrogen fluoride, potassium hydrogen fluoride, ammoniumhydrogen fluoride and mixtures thereof. Preferably, the concentration offluorine-containing material in the pretreatment coating ranges fromabout 100 to about 5200 parts per million (ppm) and more preferablyabout 300 to about 3500 ppm. Generally, the weight ratio of reactionproduct to fluoride ions ranges from about 10:1 to about 55:1.

The fluorine-containing material can be applied to the metal substrateprior to application of the treating solution or included in thetreating solution itself. If applied prior to application of thetreating solution, the pH of an aqueous solution including thefluorine-containing material generally ranges from about 2.4 to about4.0 and can be adjusted by adding sodium hydroxide.

The treating solution can further comprise one or more Group IVBelement-containing materials. The Group IVB elements are defined by theCAS Periodic Table of the Elements as shown, for example, in theHandbook of Chemistry and Physics, (60th Ed. 1980) inside cover, whichare hereby incorporated by reference, and include zirconium, titaniumand hafnium. Zirconium- and titanium-containing materials are preferred.

Preferably, the Group IVB-element containing materials are in the formof metal salts or acids which are water soluble. Non-limiting examplesof suitable zirconium-containing materials include fluorozirconic acid,potassium hexafluorozirconate, alkali salts of zirconium hexafluoride,amine salts of zirconium hexafluoride and mixtures thereof. Non-limitingexamples of suitable titanium-containing materials include fluorotitanicacid, alkali salts of hexafluorotitanate, amine salts ofhexafluorotitanate and mixtures thereof. The Group IVB-elementcontaining materials can be the source of some or all of thefluorine-containing materials discussed above.

Generally, the Group IVB element-containing material is included in thetreating solution in an amount to provide a concentration of up to about2000 ppm, and preferably about 100 to about 1000 ppm, based upon totalweight of the treating solution. Alternatively, the Group IVB-elementcontaining material can be applied to the metal substrate prior toapplication of the treating solution.

The treating solution can further comprise surfactants that function asaids to improve wetting of the substrate. Generally, the surfactantmaterials are present in an amount of less than about 2 weight percenton a basis of total weight of the treating solution.

Preferably, the treating solution is essentially free ofchromium-containing materials, i.e., contains less than about 2 weightpercent of chromium-containing materials (expressed as CrO₃), and morepreferably less than about 0.05 weight percent of chromium-containingmaterials. Examples of such chromium-containing materials includechromic acid, chromium trioxide, chromic acid anhydride, dichromatesalts such as ammonium dichromate, sodium dichromate, potassiumdichromate, and calcium, barium, magnesium, zinc, cadmium and strontiumdichromate. Most preferably, the treating solution is free ofchromium-containing materials.

In a preferred embodiment, the reaction product of an epoxy-functionalmaterial and a phosphorus-containing material is formed from EPON® 828epoxy-functional resin and phosphoric acid in an equivalent ratio ofabout 1:1.6. The reaction product is present in the treating solution inan amount of about 5 weight percent on a basis of total weight of thetreating solution. The preferred treating solution also includesdiisopropanolamine, DOWANOL PM and deionized water. A small amount ofhydrofluoric acid can be included to adjust the pH of the treatingsolution to about 5.

In an alternative preferred embodiment, the reaction product of an epoxyfunctional material and amine-containing material is formed from EPON®828 epoxy-functional resin and diethanolamine. The reaction product ispresent in the treating solution in an amount of about 400 to about 1400ppm based upon total weight of the treating solution. Zirconium ions arepreferably present, added as fluorozirconic acid, at a level of about 75to about 225 ppm based upon total weight of the treating solution. Otheradditives present include SURFYNOL® DF110 L surfactant (about 20 ppm)and monomethyl ether of dipropylene glycol (about 300 ppm). The pH ofthe treating solution is adjusted to about 4.0 to about 4.7 usingaqueous solutions of nitric acid and sodium hydroxide.

The treating solution is applied to the surface of the metal substrateby any conventional application technique, such as spraying, immersionor roll coating in a batch or continuous process. The temperature of thetreating solution at application is typically about 10° C. to about 85°C., and preferably about 15° C. to about 60° C. The pH of the preferredtreating solution at application generally ranges from about 2.0 toabout 7.0, and is preferably about 2.7 to about 6.5.

Continuous processes are typically used in the coil coating industry andalso for mill application. The treating solution can be applied by anyof these. conventional processes. For example, in the coil industry, thesubstrate is cleaned and rinsed and then usually contacted with thetreating solution by roll coating with a chemical coater. The treatedstrip is then dried by heating and painted and baked by conventionalcoil coating processes.

Mill application of the treating solution can be by immersion, spray orroll coating applied to the freshly manufactured metal strip. Excesstreating solution is typically removed by wringer rolls. After thetreating solution has been applied to the metal surface, the metal canbe rinsed with deionized water and dried at room temperature or atelevated temperatures to remove excess moisture from the coatedsubstrate surface and cure any curable coating components to form thepretreatment coating. Alternately, the treated substrate can be heatedat about 65° C. to about 125° C. for about 2 to about 30 seconds toproduce a coated substrate having a dried residue of the pretreatmentcoating thereon. If the substrate is already heated from the hot meltproduction process, no post application heating of the treated substrateis required to facilitate drying. The temperature and time for dryingthe coating will depend upon such variables as the percentage of solidsin the coating, components of the coating and type of substrate.

The film coverage of the residue of the pretreatment coating generallyranges from about 1 to about 1000 milligrams per square meter (mg/m²),and is preferably about 10 to about 400 mg/m².

In the present invention, a weldable coating is deposited upon at leasta portion of the pretreatment coating. The weldable coating comprisesone or more electroconductive pigments which provide electroconductivityand cathodic protection to the weldable coating and one or more binderswhich adhere the electroconductive pigment to the pretreatment coating.

Non-limiting examples of suitable electroconductive pigments includezinc (preferred), aluminum, iron, graphite, diiron phosphide andmixtures thereof. Preferred zinc particles are commercially availablefrom ZINCOLI GmbH as ZINCOLI S 620 or 520. The average particle size(equivalent spherical diameter) of the electroconductive pigmentparticles generally is less than about 10 micrometers, preferably rangesfrom about 1 to about 5 micrometers, and more preferably about 3micrometers.

Since the metal substrates are to be subsequently welded, the weldablecoating must comprise a substantial amount of electroconductive pigment,generally greater than about 10 volume percent and preferably about 30to about 60 volume percent on a basis of total volume ofelectroconductive pigment and binder.

The binder is present to secure the electroconductive pigment to thepretreatment coating. Preferably, the binder forms a generallycontinuous film when applied to the surface of the pretreatment coating.Generally, the amount of binder can range from about 5 to about 50weight percent of the weldable coating on a total solids basis,preferably about 10 to about 30 weight percent and more preferably about10 to about 20 weight percent.

The binder can comprise oligomeric binders, polymeric binders andmixtures thereof. The binder is preferably a resinous polymeric bindermaterial selected from thermosetting binders, thermoplastic binders ormixtures thereof. Non-limiting examples of suitable thermosettingmaterials include polyesters, epoxy-containing materials such as arediscussed above, phenolics, polyurethanes, and mixtures thereof, incombination with crosslinkers such as aminoplasts or isocyanates whichare discussed below. Non-limiting examples of suitable thermoplasticbinders include high molecular weight epoxy resins, defunctionalizedepoxy resins, vinyl polymers, polyesters, polyolefins, polyamides,polyurethanes, acrylic polymers and mixtures thereof. Examples of usefulbinder materials include phenoxy polyether polyols and inorganicsilicates.

Particularly preferred binder materials are polyglycidyl ethers ofpolyhydric phenols, such as those discussed above, having a weightaverage molecular weight of at least about 2000 and preferably rangingfrom about 5000 to about 100,000. These materials can be epoxyfunctional or defunctionalized by reacting the epoxy groups withphenolic materials. Such binders can have epoxy equivalent weights ofabout 2000 to about one million. Non-limiting examples of useful epoxyresins are commercially available from Shell Chemical Company as EPON®epoxy resins. Preferred EPON® epoxy resins include EPON®1009, which hasan epoxy equivalent weight of about 2300-3800. Useful epoxydefunctionalized resins include EPONOL resin 55-BK-30 which iscommercially available from Shell.

Suitable crosslinkers or curing agents are described in U.S. Pat. No.4,346,143 at column 5, lines 45-62 and include blocked or unblocked di-or polyisocyanates such as DESMODUR® BL 1265 toluene diisocyanateblocked with caprolactam, which is commercially available from Bayer,and aminoplasts such as etherified derivatives of urea-melamine- andbenzoguanamine-formaldehyde condensates which are commercially availablefrom Cytec Industries under the trademark CYMEL® and from Solutia underthe trademark RESIMENE®.

Preferably, the weldable coating composition comprises one or morediluents for adjusting the viscosity of the composition so that it canbe applied to the metal substrate by conventional coating techniques.The diluent should be selected so as to not detrimentally affect theadhesion of the weldable coating to the pretreatment coating upon themetal substrate. Suitable diluents include ketones such as cyclohexanone(preferred), acetone, methyl ethyl ketone, methyl isobutyl ketone andisophorone; esters and ethers such as 2-ethoxyethyl acetate, propyleneglycol monomethyl ethers such as DOWANOL PM, dipropylene glycolmonomethyl ethers such as DOWANOL DPM or propylene glycol methyl etheracetates such as PM ACETATE which is commercially available from DowChemical; and aromatic solvents such as toluene, xylene, aromaticsolvent blends derived from petroleum such as SOLVESSO®. The amount ofdiluent can vary depending upon the method of coating, the bindercomponents and the pigment-to-binder ratio, but generally ranges fromabout 10 to about 50 weight percent on a basis of total weight of theweldable coating.

The weldable coating can further comprise optional ingredients such asphosphorus-containing materials, including metal phosphates or theorganophosphates discussed in detail above; inorganic lubricants such asGLEITMO 1000S molybdenum disulfide particles which are commerciallyavailable from Fuchs of Germany; extender pigments such as iron oxidesand iron phosphides; flow control agents; thixotropic agents such assilica, montmorillonite clay and hydrogenated castor oil; anti-settlingagents such as aluminum stearate and polyethylene powder; dehydratingagents which inhibit gas formation such as silica, lime or sodiumaluminum silicate; and wetting agents including salts of sulfated castoroil derivatives such as DEHYSOL R.

Other pigments such as carbon black, iron oxide, magnesium silicate(talc), zinc oxide and corrosion inhibiting pigments including zincphosphate and molybdates such as calcium molybdate, zinc molybdate,barium molybdate and strontium molybdate and mixtures thereof can beincluded in the weldable coating. Generally, these optional ingredientscomprise less than about 20 weight percent of the weldable coating on atotal solids basis, and usually about 5 to about 15 weight percent.Preferably, the weldable coating is essentially free ofchromium-containing materials, i.e., comprises less than about 2 weightpercent of chromium-containing materials and more preferably is free ofchromium-containing materials.

The preferred weldable coating includes EPON® 1009 epoxy-functionalresin, zinc dust, salt of a sulfated castor oil derivative, silica,molybdenum disulfide, red iron oxide, toluene diisocyanate blocked withcaprolactam, melamine resin, dipropylene glycol methyl ether, propyleneglycol methyl ether acetate and cyclohexanone.

The weldable coating can be applied to the surface of the pretreatmentcoating by any conventional method well known to those skilled in theart, such as dip coating, direct roll coating, reverse roll coating,curtain coating, air and airless spraying, electrostatic spraying,pressure spraying, brushing such as rotary brush coating or acombination of any of the techniques discussed above.

The thickness of the weldable coating can vary depending upon the use towhich the coated metal substrate will be subjected. Generally, toachieve sufficient corrosion resistance for coil metal for automotiveuse, the applied weldable coating should have a film thickness of atleast about 1 micrometer (about 0.5 mils), preferably about 1 to about20 micrometers and more preferably about 2 to about 5 micrometers. Forother substrates and other applications, thinner or thicker coatings canbe used.

After application, the weldable coating is preferably dried and/or anycurable components thereof are cured to form a dried residue of theweldable coating upon the substrate. The dried residue can be formed atan elevated temperature ranging up to about 300° C. peak metaltemperature. Many of the binders such as those prepared fromepoxy-containing materials require curing at an elevated temperature fora period of time sufficient to vaporize any diluents in the coating andto cure or set the binder. In general, baking temperatures will bedependent upon film thickness and the components of the binder. Forpreferred binders prepared from epoxy-containing materials, peak metaltemperatures of about 150° C. to about 300° C. are preferred.

After the weldable coating has been dried and/or cured, the metalsubstrate can be stored or forwarded to other operations, such asforming, shaping, cutting and/or welding operations to form thesubstrate into parts such as fenders or doors and/or to a subsequentelectrocoat or topcoating. operations. While the metal is being stored,transported or subjected to subsequent operations, the coatings protectthe metal surface from corrosion, such as white and red rust, due toexposure to atmospheric conditions.

Since the coated metal substrate prepared according to the presentinvention is electroconductive, top coating of the coated substrate byelectrodeposition is of particular interest. Compositions and methodsfor electrodepositing coatings are well known to those skilled in theart and a detailed discussion thereof is not believed to be necessary.Useful compositions and methods are discussed in U.S. Pat. No. 5,530,043(relating to anionic electrodeposition) and U.S. Pat. Nos. 5,760,107,5,820,987 and 4,933,056 (relating to cationic electrodeposition) whichare hereby incorporated by reference.

The weldable coated metal substrate optionally can be coated with ametal phosphate coating, such as zinc phosphate, which is deposited uponat least a portion of the weldable coating. Methods of application andcompositions for such metal phosphate coatings are disclosed in U.S.Pat. Nos. 4,941,930 and 5,238,506, which are hereby incorporated byreference.

The pretreatment coating and weldable coating provide the metalsubstrate of the present invention with improved adhesion andflexibility and resistance to humidity, salt spray corrosion andcomponents of subsequently applied coatings. In addition, the disposaland use problems associated with chromium can be reduced or eliminated.

The present invention will now be illustrated by the following specific,non-limiting examples. All parts and percentages are by weight unlessotherwise indicated.

EXAMPLES

The following examples show the use of pretreatment coatings comprisingepoxy esters of phosphoric acid applied to steel substrates which aresubsequently coated with weldable coatings according to the presentinvention.

Preparation and Coating of Substrates

Various types of steel panels, listed in Tables 1-2 were obtained fromACT Laboratories. Each panel was about 10.16 centimeters (cm) (4 inches)wide, about 30.48 cm (12 inches) long and about 0.76 to 0.79 mm (0.030to 0.031 inches) thick. The steel panels were subjected to an alkalinecleaning process by immersion in a 2% by volume bath of CHEMKLEEN 163which is available from PPG Industries, Inc. at a temperature of 60° C.(140° F.) for 30 seconds. The panels were removed from the alkalinecleaning bath, rinsed with room temperature water (about 21° C. (70°F.)) for 5 seconds and dried with an “air-knife”.

As shown in Tables 1-2, several of the cleaned panels were leftuntreated. The remainder of the panels were treated with one of thefollowing pretreatment coatings: (1) a solution of NUPAL 435¹, whichincludes an epoxy ester of phosphoric acid and fluoride according to thepresent invention (Example 1); (2) a solution of NUPAL 510², whichincludes an epoxy ester of phosphoric acid, fluoride and fluorozirconateaccording to the present invention (Example 2); or a chromium-basedpretreatment, BONDER 1415A, available from Henkel Corporation. Allpanels treated with BONDER 1415A had a measured elemental chromiumweight of between 10 mg/m² and 20 mg/m² (1.1 mg/ft² and 2.1 mg/ft²).

¹NUPAL 435 organophosphate solution is commercially available from PPGIndustries, Inc. The concentration of the organophosphate was 1% byweight based on total weight of the solution.

²NUPAL 510 organophosphate solution is commercially available from PPGIndustries, Inc. The concentration of the organophosphate was 5% byweight based on total weight of the solution.

All pretreatment solutions were applied via roll coat application at3.4×10⁵ Pa (50 psi) and a rate of 56.4 meters/min (185 ft/min). Panelswere immediately baked for 15 seconds to a peak metal temperature of110° C.±6° C. (230° F.±10° F.). After drying, all panels were coatedwith BONAZINC 3000 zinc-rich, epoxy resin-containing weldable coating,which is commercially available from PPG Industries, Inc., on one sideof the panel with a #5 drawbar (resulting in a dried film thickness ofbetween 2.9 microns and 3.2 microns) and baked at 316° C. (600° F.) forabout 1-2 minutes until a peak metal temperature of 254° C. (490° F.)was achieved. The panels were then cooled at ambient temperature.

Adhesion and Corrosion Testing

To determine the adhesion of the coating systems under fabricationconditions, panels coated as described above and as summarized in Tables1 and 2 were coated with about 1064 mg/m² (about 100 mg/ft²) of Quaker61AUS mill oil and drawn into square cups 25.4 mm (1 inch) high and 36.5mm (1{fraction (7/16)} inches) along each side. Adhesion performance wasevaluated on areas of the cups where deformation and strain was greatest(sides and top/bottom corners). The percentage of area in which completedelamination occurred for each sample is shown in Tables 1 and 2 below.After the initial adhesion evaluation, cups were placed in corrosiontesting for the respective durations specified in Tables 1 and 2.Relative ratings according to the percentage of red rust which formedover the entire tested surface of the cup, as well as the degree ofwhite stain, are shown in Tables 1 and 2.

Two sets of corrosion tests were conducted on the fabricated cups. Eachsample was subjected to a minimum of 5 cycles and a maximum of 40 cyclesaccording to GM 9540P Cycle B Corrosion Test. Salt spray resistance wasdetermined by exposing samples of unscored cups and samples in which thefilm is scored with a carbide tip scriber instrument to expose the basemetal. The samples were then exposed to a 5% salt solution for either100 hours or 1000 hours as reported in Tables 1-2 and according to ASTMB-117.

TABLE 1 SALT SPRAY CYCLE B TESTING TESTING CUPS CUPS INITIAL % RED % REDADHESION RUST RUST CUPS (Degree of (Degree of SUBSTRATE % Coating WhiteWhite TESTED TREATMENT Loss¹ Stain)^(2,3) Stain)^(2,4) ACT EZG-60G2-sided Clean only 30 to 50% 50% 25% Electrogalvanized Steel (Heavy)(Moderate) ACT EZG-60G 2-sided Example 1  5 to 10%  4 %  6 %Electrogalvanized Steel (Moderate) (Light/Mod) ACT EZG-60G 2-sidedExample 2 <5% <1%  8% Electrogalvanized Steel (Moderate) (Light/Mod) ACTEZG-60G 2-sided Bonder  5 to 10% 10%  4% Electrogalvanized Steel 1415A(Mod/Heavy) (Light/Mod) ACT HDG-G70 70U Clean only 40 to 60% 15%  1% Hotdipped galvanized Steel (Moderate) (Light/Mod) ACT HDG-G70 70U Example 1 5 to 10%  7%  2% Hot dipped galvanized Steel (Light) (Light/Mod) ACTHDG-G70 70U Example 2  5 to 10%  5%  2% Hot dipped galvanized Steel(Light) (Light/Mod) ACT HDG-G70 70U Bonder  5 to 10% 10%  1% Hot dippedgalvanized Steel 1415A (Moderate) (Light/Mod) ACT HDA Zn/Fe-A45 2 sideClean only  5 to 10% 10%  8% Hot dipped galvanneal Steel (Light/Mod)(Light) ACT HDA Zn/Fe-A45 2 side Example 1 <5%  4%  4% Hot dippedgalvanneal Steel (Light/Mod) (Very Light) ACT HDA Zn/Fe-A45 2 sideExample 2 <5%  6% 20% Hot dipped galvanneal Steel (Light/Mod) (Light)ACT HDA Zn/Fe-A45 2 side Bonder <5%  8% 30% Hot dipped galvanneal Steel1415A (Light/Mod) (Light) ¹Values based on the range over six cups.²Values based on the average of two cups. ³EZG, HDG and HDA cups andpanels were exposed for 1000 hours. CRS cups were exposed for 100 hours.⁴EZG and HDG cups were exposed for 40 cycles. HDA cups were exposed for30 cycles. CRS cups were exposed for 5 cycles.

TABLE 2 INITIAL ADHESION SALT SPRAY CYCLE B CUPS TESTING TESTINGSUBSTRATE TREAT- % Coating CUPS CUPS TESTED MENT Loss¹ % RED RUST^(2,3)% RED RUST^(2,4) ACT CRS (unpolished) Clean only 40 to 60%  70% 75% ColdRolled Steel (N/A) (N/A) ACT CRS (unpolished) Example 1 5 to 10% 95% 85%Cold Rolled Steel (N/A) (N/A) ACT CRS (unpolished) Example 2 5 to 10%90% 85% Cold Rolled Steel (N/A) (N/A) ACT CRS (unpolished) Bonder 5 to10% 80% 80% Cold Rolled Steel 1415A (N/A) (N/A)

As shown in Tables 1 and 2 above, the steel cups of Examples 1 and 2(coated with a pretreatment coating and weldable coating according tothe present invention) had superior initial coating adhesion compared tothe controls (coated only with the weldable coating) and comparableinitial adhesion compared to steel cups coated with a commerciallyavailable chromium-containing pretreatment.

Also, the steel cups of Examples 1 and 2 prepared according to thepresent invention had generally improved salt spray corrosion resistancecompared to the clean only controls and steel cups coated with acommercially available chromium-containing pretreatment forelectrogalvanized steel, hot dipped galvanized steel and hot dippedGALVANNEAL steel. For electrogalvanized steel, the steel cups ofExamples 1 and 2 prepared according to the present invention hadsuperior Cycle B testing results when compared to the clean onlycontrols and comparable performance to steel cups coated with acommercially available chromium-containing pretreatment.

Resistance Welding Testing

The weldability of samples of the coated panels was evaluated bydetermining the lobe width of each weld using a minimum acceptablenugget diameter of 3.6 mm. The lobe width is the difference in amount ofcurrent (thousands of amps) between the amount of welding current neededto form a spot weld of a minimum acceptable size and the amount ofwelding current that is used before “expulsion” occurs. Expulsion is theviolent expulsion of molten metal from the weld, typically accompaniedby an audible sound and flying sparks. It is desirable for thisdifference, or lobe width, to be as large as possible.

After two panels of metal were spot welded, they were testeddestructively by peeling the two panels apart. Typically, a button or“nugget” remained on one of the panels, and a hole was pulled out of theother panel. The minimum acceptable diameter of the nugget wasdetermined by the thickness of the two panels and the face diameter ofthe electrodes. The coated metal panels or sheets of the presentinvention were 0.76 mm (0.030 inches) thick and the electrodes used hada face diameter of 5 mm. For these welding parameters, a minimumacceptable nugget is 3.6 millimeters in diameter. For nuggets that werenot circular, the weld nugget diameter was determined by averaging theshortest dimension of the weld nugget with its longest dimension.

Each coated panel was cut into samples approximately 50.8 mm by 25.4 mm(2 inches by 1 inch) for testing. The coated samples were aligned withthe coated surfaces of each sample facing each other on the inside, or“faying surface” of the weld. Each pair of samples was welded togetherwith two welds, each weld located approximately 12.7 mm (½ inch) fromeither end, using the same amount of welding current for each weld. Thecopper welding tips were pressed against the metal samples on theuncoated outside surfaces thereof. A resistance spot welder capable ofgenerating at least 500 pounds of force and at least 10 kiloamps ofwelding current was used to weld the panels together. The welding tipswere class II copper, 45° truncated cones with a face diameter of 5 mm.

For each of the panels, about 25 to 30 welds were made to find theapproximate amount of current suitable for the combination of metal typeand pretreatment. Then, the highest amount of welding current that couldbe used without expulsion on the second weld was determined. Immediatelyafter this determination, successive pairs of welds were made on thesamples at lower amounts of current to determine the smallest amount ofcurrent that could make a weld of at least 3.6 mm in diameter. Thewelding conditions used were: 450 pounds of force, 11 cycles ({fraction(11/60)} second) of weld current duration, and 5 cycles ({fraction(5/60)} second) of hold time after the weld current was applied. Thesecond weld of each pair of welds was used to determine nugget size andfor observing expulsion. In all cases, only the second weld of a pairwas considered to be the test weld. The difference between the maximumcurrent without expulsion and minimum current that was used to make aweld of 3.6 millimeters or larger was calculated to be the lobe width.Values of lobe width for each Example are set forth in Table 3 below.

TABLE 3 Minimum Maximum Current Current for 3.6 mm Without DiameterSUBSTRATE Expulsion Nugget Lobe Width TESTED TREATMENT (kiloamps)^(2,4)(kiloamps)^(2,4) (kiloamps)^(3,5) ACT EZG-60G 2-sided Clean only 8.9 8.20.7 Electrogalvanized Steel ACT EZG-60G 2-sided Example 1 8.4 8.1 0.3Electrogalvanized Steel ACT EZG-60G 2-sided Example 2 8.5 8.1 0.4Electrogalvanized Steel ACT EZG-60G 2-sided Bonder 8.5 8.1 0.4Electrogalvanized Steel 1415A ACT HDG-G70 70U Clean only 8.9 8.1 0.8 Hotdipped galvanized Steel ACT HDG-G70 70U Example 1 8.9 8.3 0.6 Hot dippedgalvanized Steel ACT HDG-G70 70U Example 2 8.7 8.2 0.5 Hot dippedgalvanized Steel ACT HDG-G70 70U Bonder 9.0 8.2 0.8 Hot dippedgalvanized 1415A Steel ACT HDA Zn/Fe-A45 2 Clean only 8.0 6.8 1.2 sideHot dipped galvanneal Steel ACT HDA Zn/Fe-A45 2 Example 1 7.9 6.8 1.1side Hot dipped galvanneal Steel ACT HDA Zn/Fe-A45 2 Example 2 8.8 7.51.3 side Hot dipped galvanneal Steel ACT HDA Zn/Fe-A45 2 Bonder 8.0 6.91.1 side 1415A Hot dipped galvanneal Steel

As shown in Table 3, samples of various types of steel coated withweldable coatings according to the present invention had comparable lobewidth values to a sample pretreated with a commercially availablechromium-containing pretreatment.

Similar weld testing was performed on samples of British Steel and VoestAlpine steel which were cleaned and coated as discussed above. Onesample was pretreated with GRANODINE 4513 chromium-containingpretreatment, which is commercially available from Henkel. MB-Standardelectrodes F16 having a diameter of 5.5 mm flat were used to perform thewelding. The welding time was conducted according to DVS 2902.Part 4 andelectrode power was conducted according to DVS 2904 Part 4 plus maximum25%. The results of this weld testing are set forth in Table 4 below.

TABLE 4 COMMERCIAL Lobe Width SUBSTRATE TESTED TREATMENT (kiloamps)British Steel Example 1 2.6 Electrogalvanized Steel British Steel Bonder1.5 Electrogalvanized Steel 1415A Voest Alpine 75/75 Example 1 1.6Electrogalvanized Steel Voest Alpine 75/75 Example 2 1.6Electrogalvanized Steel Voest Alpine 75/75 GRANODlNE 0.9Electrogalvanized Steel 4513

As shown in Table 4, electrogalvanized steel samples coated withweldable coatings according to the present invention had higher lobewidth values than samples pretreated with two commercially availablechromium-containing pretreatments.

The metal substrates of the present invention have coatings thereonwhich can provide corrosion protection in areas which are difficult forconventional electrocoat treatments to reach. This enhanced corrosionprotection can reduce or eliminate the need for wax fillers and sealersin automotive parts, such as door hem flanges. The coatings maintainelectroconductivity of the metal substrate to facilitate welding orelectrodeposition of subsequent coatings. The coatings also providelubricity to assist in forming and stamping of parts prepared from thecoated metal substrate. These coatings can be applied at the metalforming or steel mill to protect the coated substrate from corrosion anddamage during transportation and fabricating operations.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications which are within the spirit and scopeof the invention, as defined by the appended claims.

Therefore, we claim:
 1. A weldable, coated metal substrate comprising:(a) a bare metal substrate; (b) a pretreatment coating having less than0.05 weight percent of chromium-containing materials, the pretreatmentcoating comprising a β-hydroxy phosphorous ester that is the reactionproduct of at least one epoxy-functional material and aphosphorus-containing material deposited upon at least a portion of asurface of the metal substrate; and (c) a weldable coating comprising anelectroconductive pigment and a binder deposited upon at least a portionof the pretreatment coating.
 2. The coated metal substrate according toclaim 1, wherein the metal substrate comprises a ferrous metal.
 3. Thecoated metal substrate according to claim 2, wherein the ferrous metalis selected from the group consisting of iron, steel, and alloysthereof.
 4. The coated metal substrate according to claim 3, wherein theferrous metal comprises steel selected from the group consisting of coldrolled steel, galvanized steel, electrogalvanized steel, stainlesssteel, and combinations thereof.
 5. The coated metal substrate accordingto claim 1, wherein the metal substrate comprises a non-ferrous metalselected from the group consisting of aluminum, zinc, magnesium, andalloys thereof.
 6. The coated metal substrate according to claim 1,wherein the epoxy-functional material is the condensation reactionproduct of an epihalohydrin with a polyhydric alcohol.
 7. The coatedmetal substrate according to claim 1, wherein the phosphorus-containingmaterial is selected from the group consisting of phosphoric acids,phosphonic acids, and mixtures thereof.
 8. The coated metal substrateaccording to claim 1, wherein the reaction product is selected from thegroup consisting of epoxy esters of phosphoric acid, epoxy esters ofphosphonic acid, and mixtures thereof.
 9. The coated metal substrateaccording to claim 1, wherein the pretreatment coating further comprisesat least one secondary amine.
 10. The coated metal substrate accordingto claim 9, wherein the secondary amine is diisopropanol amine.
 11. Thecoated metal substrate according to claim 1, wherein the pretreatmentcoating further comprises a fluorine-containing material.
 12. The coatedmetal substrate according to claim 11, wherein the fluorine-containingmaterial is selected from the group consisting of hydrofluoric acid,fluorosilicic acid, sodium hydrogen fluoride, potassium hydrogenfluoride, ammonium hydrogen fluoride, and mixtures thereof.
 13. Thecoated metal substrate according to claim 1, wherein the pretreatmentcoating further comprises at least one Group IVB element-containingmaterial.
 14. The coated metal substrate according to claim 13, whereinthe Group IVB element-containing material is a zirconium-containingmaterial selected from the group consisting of fluorozirconic acid,potassium hexafluorozirconate, alkali salts of zirconium hexafluoride,amine salts of zirconium hexafluoride, and mixtures thereof.
 15. Thecoated metal substrate according to claim 13, wherein the Group IVBelement-containing material is a titanium-containing material selectedfrom the group consisting of fluorotitanic acid, alkali salts ofhexafluorotitanate, amine salts of hexafluorotitanate, and mixturesthereof.
 16. The coated metal substrate according to claim 1, whereinthe electroconductive pigment is selected from the group consisting ofzinc, aluminum, iron, graphite, diiron phosphide, and mixtures thereof.17. The coated metal substrate according to claim 1, wherein the binderis selected from the group consisting of oligomeric binders, polymericbinders, and mixtures thereof.
 18. The coated metal substrate accordingto claim 1, wherein the binder is selected from the group consistingthermosetting binders, thermoplastic binders, and mixtures thereof. 19.The coated metal substrate according to claim 18, wherein the bindercomprises a thermosetting binder selected from the group consisting ofpolyesters, epoxy-containing materials, phenolics, aminoplasts,polyurethanes and mixtures thereof.
 20. The coated metal substrateaccording to claim 19, wherein the binder comprises an epoxy-containingmaterial which is a polyglycidyl ether of bisphenol A.
 21. The coatedmetal substrate according to claim 19, wherein the weldable coatingfurther comprises a crosslinker for crosslinking the thermosettingbinder.
 22. The coated metal substrate according to claim 18, whereinthe binder comprises a thermoplastic binder selected from the groupconsisting of vinyl polymers, polyesters, polyolefins, polyamides,polyurethanes, acrylic polymers, and mixtures thereof.
 23. The coatedmetal substrate according to claim 1, wherein the weldable coatingfurther comprises a phosphorus-containing material.
 24. The coated metalsubstrate according to claim 1, wherein the weldable coating furthercomprises an inorganic lubricant.
 25. The coated metal substrateaccording to claim 24, wherein the inorganic lubricant is molydenumdisulfide.
 26. The coated metal substrate according to claim 1, whereinthe coated metal substrate further comprises a metal phosphate coatingdeposited upon at least a portion of the weldable coating.
 27. Thecoated metal substrate according to claim 1, wherein the coated metalsubstrate further comprises an electrodeposited coating deposited uponat least a portion of the weldable coating.
 28. A weldable, coated metalsubstrate comprising: (a) a bare metal substrate; (b) a pretreatmentcoating having less than 0.05 weight percent of chromium-containingmaterials, the pretreatment coating comprising a reaction product of atleast one epoxy-functional material and a phosphorus-containing materialdeposited upon at least a portion of a surface of the metal substrate;and (c) a weldable coating comprising an electroconductive pigment and abinder deposited upon at least a portion of the pretreatment coating,wherein the epoxy functional material is a polyglycidyl ether ofbisphenol A.